Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle or large-sized devices, such as vehicles, use a middle or large-sized battery module having a plurality of battery cells electrically connected to each other because high power and large capacity are necessary for the middle or large-sized devices.
Preferably, the middle or large-sized battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the middle or large-sized battery module. In particular, much interest is currently generated in the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the pouch-shaped battery is lightweight, the manufacturing cost of the pouch-shaped battery is low, and it is easy to modify the shape of the pouch-shaped battery.
In order for the middle or large-sized battery module to provide power and capacity required by a predetermined apparatus or device, it is necessary for the middle or large-sized battery module to be configured to have a structure in which a plurality of battery cells is electrically connected in series to each other, and the battery cells are stable against external force.
Also, the battery cells constituting the middle or large-sized battery module are secondary batteries which can be charged and discharged. Consequently, a large amount of heat is generated from the high-power, large-capacity secondary battery during the charge and discharge of the secondary battery. If the heat, generated from the unit cells during the charge and discharge of the unit cells, is not effectively removed, the heat accumulates in the respective unit cells with the result that deterioration of the unit cells is accelerated. According to circumstances, the unit cells may catch fire or explode. For this reason, a cooling system is needed in a battery pack for vehicles, which is a high-power, large-capacity battery, to cool battery cells mounted in the battery pack.
Meanwhile, a conventional battery pack is configured to have a structure in which a plurality of battery cells is stacked in one direction or a lateral direction so that the battery cells are arranged in the stacked direction. The battery pack is generally formed in the shape of a rectangular parallelepiped, which can be properly installed in a trunk of a vehicle or a space under a seat of the vehicle.
Since the structure of the conventional battery pack is generally formed in the shape of the rectangular parallelepiped, however, it is difficult to install the battery pack when the battery pack is installed is the lower part of the vehicle.
Therefore, there is a high necessity for a battery pack that can be easily installed even when a battery pack installation space is the lower part of a vehicle and that has a cooling structure to uniformly maintain internal temperature of the battery pack.